 /*
  * $Header: /cvshome/build/org.osgi.service.wireadmin/src/org/osgi/service/wireadmin/Producer.java,v 1.10 2006/07/11 00:54:10 hargrave Exp $
  *
  * Copyright (c) OSGi Alliance (2002, 2006). All Rights Reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  * http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 package org.osgi.service.wireadmin;

 /**
  * Data Producer, a service that can generate values to be used by
  * {@link Consumer} services.
  *
  * <p>
  * Service objects registered under the Producer interface are expected to
  * produce values (internally generated or from external sensors). The value can
  * be of different types. When delivering a value to a <code>Wire</code> object,
  * the Producer service should coerce the value to be an instance of one of the
  * types specified by {@link Wire#getFlavors}. The classes are specified in
  * order of preference.
  *
  * <p>
  * When the data represented by the Producer object changes, this object should
  * send the updated value by calling the <code>update</code> method on each of
  * <code>Wire</code> objects passed in the most recent call to this object's
  * {@link #consumersConnected} method. These <code>Wire</code> objects will pass
  * the value on to the associated <code>Consumer</code> service object.
  *
  * <p>
  * The Producer service may use the information in the <code>Wire</code> object's
  * properties to schedule the delivery of values to the <code>Wire</code> object.
  *
  * <p>
  * Producer service objects must register with a <code>service.pid</code> and a
  * {@link WireConstants#WIREADMIN_PRODUCER_FLAVORS} property. It is recommended
  * that a Producer service object also registers with a
  * <code>service.description</code> property. Producer service objects must
  * register with a {@link WireConstants#WIREADMIN_PRODUCER_FILTERS} property if
  * the Producer service will be performing filtering instead of the
  * <code>Wire</code> object.
  *
  * <p>
  * If an exception is thrown by a Producer object method, a
  * <code>WireAdminEvent</code> of type {@link WireAdminEvent#PRODUCER_EXCEPTION}
  * is broadcast by the Wire Admin service.
  *
  * <p>
  * Security Considerations. Data producing bundles will require
  * <code>ServicePermission[Producer,REGISTER]</code> to register a Producer
  * service. In general, only the Wire Admin service should have
  * <code>ServicePermission[Producer,GET]</code>. Thus only the Wire Admin service
  * may directly call a Producer service. Care must be taken in the sharing of
  * <code>Wire</code> objects with other bundles.
  * <p>
  * Producer services must be registered with scope names when they can send
  * different types of objects (composite) to the Consumer service. The Producer
  * service should have <code>WirePermission</code> for each of these scope names.
  *
  * @version $Revision: 1.10 $
  */
 public interface Producer {
     /**
      * Return the current value of this <code>Producer</code> object.
      *
      * <p>
      * This method is called by a <code>Wire</code> object in response to the
      * Consumer service calling the <code>Wire</code> object's <code>poll</code>
      * method. The Producer should coerce the value to be an instance of one of
      * the types specified by {@link Wire#getFlavors}. The types are specified
      * in order of of preference. The returned value should be as new or newer
      * than the last value furnished by this object.
      *
      * <p>
      * Note: This method may be called by a <code>Wire</code> object prior to this
      * object being notified that it is connected to that <code>Wire</code> object
      * (via the {@link #consumersConnected} method).
      * <p>
      * If the Producer service returns an <code>Envelope</code> object that has an
      * unpermitted scope name, then the Wire object must ignore (or remove) the
      * transfer.
      * <p>
      * If the <code>Wire</code> object has a scope set, the return value must be
      * an array of <code>Envelope</code> objects (<code>Envelope[]</code>). The
      * <code>Wire</code> object must have removed any <code>Envelope</code> objects
      * that have a scope name that is not in the Wire object's scope.
      *
      * @param wire The <code>Wire</code> object which is polling this service.
      * @return The current value of the Producer service or <code>null</code> if
      * the value cannot be coerced into a compatible type. Or an array
      * of <code>Envelope</code> objects.
      */
     public Object polled(Wire wire);

     /**
      * Update the list of <code>Wire</code> objects to which this
      * <code>Producer</code> object is connected.
      *
      * <p>
      * This method is called when the Producer service is first registered and
      * subsequently whenever a <code>Wire</code> associated with this Producer
      * becomes connected, is modified or becomes disconnected.
      *
      * <p>
      * The Wire Admin service must call this method asynchronously. This implies
      * that implementors of a Producer service can be assured that the callback
      * will not take place during registration when they execute the
      * registration in a synchronized method.
      *
      * @param wires An array of the current and complete list of <code>Wire</code>
      * objects to which this Producer service is connected. May be
      * <code>null</code> if the Producer is not currently connected to any
      * <code>Wire</code> objects.
      */
     public void consumersConnected(Wire[] wires);
 }

